Walter Kirn wrote the novel “Up in the Air,” which was adapted into the acclaimed George Clooney movie of the same name — and don’t you forget it. Kirn was the razor-sharp fiction critic for New York magazine who eviscerated almost every book he reviewed. And now he’s angry with movie critics who fail to prominently mention his contribution to the film. Kirn has been posting the reviews on his Facebook page. One of his 1,200 friends, Agustin Maes, suggested he should just be thankful that the movie’s a success. Kirn “defriended me . . . because I inadvertently aggravated his already bruised ego,” Maes posted. Another friend fumed, “How dare you suggest gratitude and perspective! You [bleep]ing bastard.” Kirn has since removed the posts.